In general, various forms of leaching copper sulfide ore by hydrometallurgy are known, such as forms of:
1) leaching copper with sulfuric acid or hydrochloric acid via a batch-wise stirring reaction; and
2) forming a stack of ores and supplying sulfuric acid or hydrochloric acid from the top of heaped ores and collecting liquid droplets dropped by the force of gravity (commonly referred to as heap leaching).
Besides, a method is also known in which force of bacteria, for example, iron-oxidizing microorganisms is utilized to leach and recover copper more efficiently (commonly referred to as bioleaching).
Bioleaching, one approach of hydrometallurgy for copper sulfide ore, has been put in practice to recover copper from secondary copper sulfide ore, such as chalcocite and covellite. However, if bioleaching is normally conducted at ambient temperature, bioleaching has a problem of a significantly low leaching rate due to extremely low solubility of primary copper sulfide ore such as chalcopyrite in inorganic acid.
To solve this problem, examples are reported in Japanese Patent No. 4565025 (hereafter referred to as PTL 1) and Japanese Patent No. 4950257 (hereafter referred to as PTL 2) in which leaching of copper from a copper sulfide ore containing primarily chalcopyrite or enargite is facilitated at ambient temperature under co-existence of iodide ion and iron(III) ions, wherein iron(III) ions are an oxidant. On the above occasion, with regard to iron(III) ions to be used as the oxidant, if iron(II) ions resulted from the leaching reaction can be oxidized to iron(III) ions and supplied again, such a case is economically desirable. Further, it is economically and environmentally desirable that a post-leaching solution preferably is also recycled as the immersion solution without being disposed of.
There are various methods to oxidize iron(II) ions to iron(III) ions, but it is preferable that a method of using iron-oxidizing microorganisms which can be applied under milder conditions, and are excellent in terms of cost. However, iodine contained in the post-leaching solution has high bactericidal properties to the iron-oxidizing microorganisms, thus tending to make it more difficult to regenerate iron (III) ions from the post-leaching solution containing iodine by using iron oxidizing microorganisms.
Accordingly, Japanese Patent No. 5571416 (hereafter referred to as PTL 3) has proposed a method for leaching copper from copper sulfide ore, wherein, upon leaching copper from copper sulfide ore using a sulfuric acid solution containing iodide ions, along with an excess amount of iron(III) ions relative to the iodide ions is used as a leaching solution, the solution obtained after the copper leaching process is treated with activated carbon to lower the concentration of iodine therein to a level less than 1 mg/L, and then iron(II) ions in the solution after copper is recovered are oxidized to iron(III) ions by the iron-oxidizing microorganisms, and then mixed with an aqueous solution containing the post-iron oxidizing solution and iodine, and used as the leaching solution for copper sulfide ore. However, such a method has had problems in which, for example, as described in Japanese Patent No. 5296126 (hereafter referred to as PTL 4), particular culture apparatus is necessary for propagation of iron-oxidizing microorganisms, and in order to avoid an influence on growth of the iron-oxidizing microorganisms, a concentration of iodine which is bactericidal needs to be lowered to a level less than 1 mg/L.